1. Technical Field
The present invention relates generally to an evaporative emission control system for automotive vehicles designed to capture fuel vapors evaporated within a fuel tank for preventing the fuel vapors from escaping outside the vehicle, and more particularly an improved structure of a canister for use in an evaporative emission control system.
2. Background of Related Art
Automotive vehicles are typically equipped with an evaporative emission control system having a canister filled with an adsorbent such as activated carbon which captures therein fuel vapors generated from a fuel tank and then releases them to an intake air pipe when the engine starts for preventing the fuel vapors from escaping out of the vehicle.
In order to meet new On-board Refueling Vapor Recovery (ORVR) regulations in the U.S., it is necessary to minimize the resistance to vapor flow in an ORVR line during refueling. For example, this line resistance may be reduced by mounting a canister, which is usually installed within an engine compartment, adjacent a fuel tank to shorten the ORVR line extending between the fuel tank and the canister.
However, most areas or spaces around the fuel tank within which the canister can be mounted are usually of limited depth flat in cross section. Additionally, conventional canisters, as taught in Japanese Utility Model First Publication Nos. 62-20159 and 63-82062, are circular in cross section and difficult to install within the flat space. The installation of such canisters near the fuel tank requires reduction in sectional area of the canisters, but it will lead to a decrease in fuel vapor adsorbing area, resulting in a lowering of vapor-absorbing ability.
During refueling, a large amount of fuel vapor is usually discharged outside the vehicle. In order to avoid an excessive rise in pressure within the fuel tank during refueling, the loss of pressure of the fuel vapor flowing through the canister also needs to be low sufficiently. Further, there is an increasing need for increasing the density of adsorbent of the canister for capturing a large amount of fuel vapor.